The invention relates to a method for producing an electrical connection between a flexible printed-circuit board and a metallic mating contact member; the electrical connection site realized between said elements; and an arrangement which makes use of such an electrical connection site for installation in an engine or a gearbox of a motor vehicle.
A large number of connection techniques for connecting electrical components to a flexible printed-circuit board are known in the art. One such method for realizing a welded joint between a flexible printed-circuit board and a metallic conductor is described in U.S. Pat. No. 5,676,865. In this method, opposite openings are made in the bottom and top insulating layers of the flexible printed-circuit board, so that a conductor track running in between is exposed on both sides in the regions of the openings. The exposed conductor track is provided with a central hole. The edge of the hole of the conductor track then undergoes a forming operation in such a way that it comes into contact with the electrical conductor on which the flexible printed-circuit board is resting with its base. Finally, the conductor track is welded onto the conductor by means of a laser in the region of the hole.
One problem with this method is that occasionally, on account of the central hole, there is insufficient conductor track material for a secure and permanent welded joint. Furthermore, bending down of the edge of the hole onto the conductor, as disclosed, presents technical problems.
Another connection method is disclosed in EP 0 163 581 B1, wherein an electrical connection is formed by a bent, flexible, two-layer connecting printed-circuit board between two parallel printed-circuit boards which are separated by a heat sink. The two parallel printed-circuit boards each have a projecting contact piece, which is soldered to an exposed contact point of the printed-circuit board. However, it is not possible to produce a welded join between the flexible two-layer printed-circuit board and the contact piece.
The present invention provides a method for producing an electrical connection between a flexible printed-circuit board and a metallic mating contact member which can be carried out easily and inexpensively and at the same time results in a mechanically stable and electrically safe connection. Further, the connection sites created by the novel method are also suitable for electrically bonding electrical components under aggravated ambient conditions, as are encountered in a gearbox or engine of a motor vehicle.
Close bearing or contiguous contact between the conductor track and the connecting section of the metallic mating contact member are required for the subsequent laser welding/soldering. This is reliably ensured, since the opening width of the connecting opening is dimensioned such that it is greater than the lateral dimensions of the connecting section of the metallic mating contact member, and hence the latter can be brought up to the exposed conductor track without any problem. The conductor track remains planar, i.e. it does not have to undergo any forming operations. During welding, the conductor track quickly melts in a central region, ensuring that adequate material is available for the building up of a stable welded joint. Because of the good thermal contact between the melted conductor track material and the connecting section of the mating contact member, the latter also melts.
Where a soldered joint is required, a soldering material is additionally provided in a way known per se between the conductor track and the connecting section. The soldering material may be deposited, for example, as an end layer of solder on the connecting section on the conductor track.
In a preferred embodiment of the method according to the present invention, a through-hole penetrating the conductor track, having smaller lateral dimensions than the width of the connecting opening, is formed between the connecting opening and an illumination aperture. A projection provided on the connecting section of the mating contact member is led through the through-hole. During the welding operation, the laser light radiates directly onto the projection, which then melts, flows onto the conductor track and together with the latter results in the welded joint by melting of the conductor track. The projection consequently represents a xe2x80x9csupply of welding materialxe2x80x9d for the creation of the connection. In a soldering operation, the soldering material may be deposited on the projection or on the conductor track.
It has been found that no additional absorption layer is required on the side of the conductor track irradiated by the laser light in order for sufficient energy for the melting of the conductor track to be coupled during the welding process.
In the production of the flexible printed-circuit board, it is preferred to apply an organic anticorrosive layer to the conductor track and thereby covering the conductor track within the light-radiating opening. Undesired surface oxidation of the conductor track in the region of the opening is also avoided by this anticorrosive layer.
The conductor track preferably has a thickness of between 40 and 150 xcexcm, and preferably between 50 and 70 xcexcm. It has been found that, in this thickness range, high-quality welded joints can be achieved largely without any problems.
The method according to the invention is used with particular advantage for the direct electrical bonding of contact pins or terminal pins of an electrical component to the flexible printed-circuit board.
An important technical application of the electrical connection site according to the present invention is the bonding of electrical components which are associated with a control device in an engine or gearbox of a motor vehicle. For such xe2x80x9cmechatronicxe2x80x9d control systems, as they are known, there has recently been developed a technical concept in which an electronic circuit accommodated in the control device housing is in electrical connection with the electrical components via a flexible printed-circuit board led through a sealing gap in the housing to the outside. Details of the construction with regard to the connection between the electronic circuit and the flexible printed-circuit board and the housing bushing are described in WO 98/44593 and are incorporated herein by reference. In this context, the electrical connection site according to the present invention consequently provides a suitable (and inexpensive) way of connecting the electrical components (sensors, actuators, etc.) present in the gearbox (engine) directly, (without component connectors or the like) to the flexible printed-circuit board, such that the connection is able to withstand the ambient conditions encountered in a gearbox (engine) (temperature range of approximately xe2x88x9240xc2x0 C. to 150xc2x0 C., and vibrations up to approximately 40 g).